Generally, power generation (the generation of electricity) has been conducted by evaporating water by using fossil fuel energy and rotating a rotor by using the evaporated vapor. However, in recent years, due to the rapid depletion of fossil fuel energy, studies on alternative energy are actively progressing. These studies are focusing on using water power and wind power to generate power, both of which are in the limelight of the world as types of alternative energy. The use of alternative energy is important the replacement of the simply provided energy source as well as to effectively generate power from the provided energy source.
Power generation from the above-mentioned energy source is realized by generators, for example, revolving armature type generators that are widely used as a direct current generator and revolving field type generators that are widely used as an alternating current (AC) generator.
The revolving armature type generator is a generator in which a magnetic field stops and a conductor rotates, on the contrary, while the revolving field type generator is a generator in which a conductor stops and a magnetic field rotates. In addition, there is a generator, in which a field coil, a rectifier, and a three-phase power source for the rectifier all are accommodated into the rotor, as the AC generator. This generator is called a brushless AC generator. Since the brushless AC generator did not have a slip ring and a brush, abrasion or exchange of the brush has not occurred, and thus it is being mainly used for high-capacity generators due to easily repair the generator.
Also, conventional generators generates the electricity so as to have rated power generation suitable for installed locations to generate power when a rotational force occurs in a predetermined range.
However, in case of a large-scaled generator, the generator demands a rotational force having predetermined magnitude or more for generating power because a large capacity generator has a great heavy weight in a rotating shaft itself. That is, in case of the large-scaled generator, in addition to the weight of the rotating shaft itself, the rotating shaft may be put on weight by a gear box installed for increasing power generation. Thus, it is difficult to initially operate the generator, and a lot of noises occur. As a result, if a rotational force less than the magnitude of a rotational force for stating of the power generation is supplied to the generator, the conventional generator having the conventional heavy rotating shaft may not be rotated or do not generate power even though the rotating shaft rotates, then the supplied rotational force may be dissipated without being contributed to the power generation. Moreover, if a rotational force greater than the rated power generation is supplied, then the power generation of the generator may exceed its limit of the amount of power generation. Thus, the surplus rotational force may not be contributed to the power generation and may be dissipated. Thus, there is a disadvantage in that the rotational force less than that for the starting of the power generation or the surplus rotational force is not utilized.
In recent years, various methods for maximizing the power generation efficiency are being studied. For example, the permanent magnet type generators are provided in plurality to generate high power generation efficiency when the rotational force is generated. Nevertheless, the method has disadvantages that the initial behavior is difficult due to resistance in installation of a plurality of the generators and the weight of rotating shaft. Also, even if the rotating shaft rotates, there is a disadvantage that the power generation is not yet realized until a sufficient rotational force is generated. Furthermore, in the conventional generator, there is a disadvantage that the rotational force less than that for starting of the power generation is not utilized.